Lake Whillans is one of about 400 sub glacial lakes under the ice, filling up with water from inland.

Priscu's team broke into Lake Whillans last year, using hot water to melt a 60-centimetre-diametre hole through the ice. The water was kept sterile using filters, heating, ultraviolet light and hydrogen peroxide.

New Scientist says that should lay to rest any suggestion that the microbes found were contaminants from the surface.

The team found 3931 species of single-celled organisms. Most seem to be feeding on sediments on the lake bed, laid down when the area was last ice-free and under the ocean, at least 120,000 years ago.

Many of the microbes convert ammonium to nitrite, according to New Scientist.

The scientists say each lake may be different.

"We've got to get down and sample these lakes," says Priscu.

The Smithsonian Magazine says the discoveries confirm that life finds a way to survive in such extreme environments, and it boosts the possibility that some form of life could be alive right now on icy moons across the solar system, such as Jupiter's moon Europa.

"An outstanding question has been whether or not the environment at the base of the ice sheet is actually suitable for microbial life to persist," Brent Christner, a microbiologist at Louisiana State University in Baton Rouge, told the magazine.

Once they reached the lake they sampled both water and sediment from the lake bottom. In a field lab, they were able to work up a genetic and chemical profile of the lake environment and its inhabitants.

Scientists report in Nature that many of their findings are new to science, but only further genetic analysis will tell for sure.

Smithsonian Magazine says there are still a host of unanswered questions about the residents of Lake Whillans and how they contribute to the ecosystem of the Ross Sea and the larger Southern Ocean.